John Patrick Monahan and John Patrick Hooper are one and the same person. He was born the son of John Manahan/Monahan (1846-1870) and Mary Donoher (various spellings) (1849-Abt 1902). Based on available records, Mary immigrated to the United States in 1852 with her family and John and Mary were married in December 1869. John Manahan, John's biological father, died in November 1870, just before the birth of his son. Mary Monahan married William Wilson Hooper in 1874 and the young John Monahan lived with the couple until he went out on his own, sometime before he married in 1896. He used the surname Monahan in the 1900 and 1910 Federal Census as did his children and wife, but before 1920, he began using the Hooper surname of his step-father. Civil records help support these facts. Most of John Patrick's descendants use the Hooper surname. John Patrick Hooper's name change occurred not long after his mother's death. The family of his mother's second husband would have been the only family he would have known and the names of several of his own sons (William & Harry) are similar to those of his step-brothers.
It may also be noted that there is also a discrepancy between the death date on John Patrick Hooper's tombstone (1950) and his Tennessee death certificate (1952).

John Monahan married Lena Norman - 4 Oct 1895 Houston County, Tennessee

1900 Humphreys County, TN Census
James M Norman 56 Head
Elizabeth J Norman 54 Wife
Daniel M Norman 22 Son
John E Norman 20 Son
Mary J Norman 16 Daughter
Wilson C Norman 14 Son
Elena E Monahan 27 Daughter
John Monahan 29 Son-in-law - Stenographer
John D Monahan 1 Grandson
Katie E Monahan 2/12 Granddaughter
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1910 Franklin County, TN Census
John Monahan 39 Head - Stove Mill Inspector
Elenah Monahan 37 Wife
John D Monahan 11 Son
William M Monahan 7 Son
Mary J Monahan 4 Daughter
Lottie P Monahan 2 Daughter
Neil Norma 23 Boarder
John Christian 32 Boarder
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1920 Decatur, Morgan County, AL Census
John P Hooper 48 Head (widowed) Lumber Mill
John D Hooper 21 Son - Lumber Mill
Mike H Hooper 17 Son - Lumber Mill
Pauline L Hooper 11 Daughter
Harry S Hooper 8 Son
Sadie L Hooper 6 Daughter
Ruthie V Hooper 3 Daughter